This blog is dedicated to bringing World War II era documents to the general public, with an overall focus on armoured warfare.
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Monday, 31 March 2014

"There are two ways to follow comrade Stalin's orders of creating a new high powered regimental gun while maintaining the weight of the old regimental gun.

The first solution: swap the barrel of the old gun. This design decision lengthens the barrel by 690 mm. The new barrel, combined with an increased charge, provides a muzzle velocity of 515 m/s, with a 6.23 kg shell. According to calculations, at 500 meters, against armour with coefficient 2400 at a 30 degree angle, the shell penetration will be 39 mm, and maximum range 8500 meters. The increased power is possible due to the use of a muzzle brake.

This solution provides immediate production of more powerful regimental guns based on existing guns, as the changes to the production process are insignificant. Furthermore, it is possible to replace the barrels on old regimental guns in the field.

The second solution is to use the blueprints we have already developed and began production of. This prototype has muzzle velocity of 550 m/s, and range of 9500 m. The new gun weighs about 100 kg less than the old one. The rate of fire is increased due to the use of a semi-automatic breech from the regimental gun. This gun is smaller than the old one.

The gun will also be simpler to produce than the old one. The re-barreled old gun and the new gun will use the same shell.

Please advise on urgent government trials of the first prototype of the re-barreled gun."

The "old gun" is the 76.2 mm model 1927 regimental gun. Here is a photograph of the modernized re-barreled gun:

Engineers of the NKVD's 4th Special Department produced a proposal for modernizing the 76 mm model 1927 regimental cannon by means of replacing its barrel with a 122 mm mono-block.

According the the calculations of the specialists, the modernized gun will greatly increase the effectiveness of the shells against pillboxes, enemy personnel, and tanks protected with up to 90 mm of armour.

I consider this proposal realizeable, and have given an order for calculations to be made and a technical project developed. I send you a copy of the explanatory memo, and would like to know your preliminary conclusion regarding the sensibility of this project.

Attachment: short explanatory memo on 3 pages.

Chief of the 4th NKVD Special Department, Senior Major of State Security, Kravchenko

Short Explanatory Memo on the Subject of Modernization of the 76 mm Regimental Gun model 1927 by Turning it into a 122 mm Mortar

Stock armour-piercing shells from the 76 mm gun can penetrate 25-30 mm of armour. HEAT shells, at the current time, can penetrate up to 60 mm of tank armour, by forming a breach of no more than 20 mm.

Using a 122 mm monoblock barrel, penetration of up to 90 mm will be achieved, with a 30 mm breach. In 60 mm armour, the shells will form a breach 50-60 mm on entry, 90-100 on exit (exploding a 107 mm shell on armour results in a 60 mm breach on entry and 80 mm on exit).

The above data shows that the regimental cannon's anti-armour capacity can be greatly raised if it turned into a 122 mm mortar.

A HEAT shell for this weapon would weigh 13.5 kilograms, with 3 kg of explosive filler. The range, with an elevation angle of 24 degrees and 30 minutes will be approximately 3.5 km, and 4.25 km with an angle of elevation of 45 degrees.

Alongside the anti-tank performance, performance against infantry and pillboxes will also grow. If the 76 mm shell had 5.8 kg of metal and 0.6 kg of explosives, the 122 mm shell has 10 kg of metal and up to 3 kg of explosives.

Modernizing the 76 mm gun into a 122 mm mortar requires only the replacement of its 76 mm monoblock barrel with a 122 mm monoblock barrel, with no changes to the recoil mechanisms or mount.

The center of gravity is preserved. The recoil mechanisms can take 350 kg (the previous weight was 304 kg). This gives the muzzle velocity of the 13.5 kg shell as 230 m/s.

Only the piston changes in the gun's breech. The front part of the piston will increase in diameter, but the part that attaches to the frame will not change. This allows the frame and associated breech components to remain the same. The length of the piston does not change, so the firing mechanism may also be retained.

The extractor should be shortened due to the increase in diameter of the brass. Due to this shortening, due to the significant decrease of weight and length of the shell (pressure of gases decreases to 500 kg/cm^2), the extractor shoulder is sufficient.

A single piece shell, which differs little in weight compared to the 76 mm shell, but is much shorter, should maintain existing rate of fire.

During the investigation of this proposal, a 107 mm variant was considered. With a 9.8 kg shell, the range at 24 degrees and 30 minutes is 4.75 kg, and 5.9 km with an angle of 45 degrees. Using stock 17 kg shells, the range is 2.2 and 3 km respectively. The penetration was experimentally determined to be 70 mm.

We decided on the 122 mm variant due to a higher penetration (90 mm) and better damage to space behind the armour, as well as higher explosive-fragmentation effect on enemy personnel and fortifications.

Sunday, 30 March 2014

The Western Wall (known also as the Siegfried Line) was a line of long term fortifications placed in the border parts of Western Germany. The line was 630 km long and 35-100 km deep. 16,000 fortifications were spread through this area.

In propaganda, the Siegfried Line was shown as impenetrable and indestructible. Battles over it began in August of 1944, and ended only on March 25th, 1945. Combat in this region was fierce. The Germans resisted desperately, the Allies took losses and experienced supply problems. Due to the inevitable end of the war, it was more and more difficult to get the soldiers to attack. No one wanted to die on the eve of victory.

In December, the Germans delivered a counteroffensive in the Ardennes. It was only dealt with by the Allies in January. Taking advantage of the Germans' defeat, the commander of the Allied forces, D. Eisenhower, gave an order to break through the Siegfried line. In February, the Rur Dam was captured, alleviating a hazard for the Allied offensive, as the Germans could open the dam and flood the Rur valley at any moment.

By March, the Allies pushed the Germans to the line itself. On March 15th, the Americans began a decisive offensive. The 7th Army crossed the Mosel river and Patton's tank forces delivered a crushing blow in the South-West direction with the intention to cut off German forces between Merzig and Saarbrücken. The 7th Army cut into the German lines and reached Kaiserslautern by March 18th, crushing and displacing the Germans. In the same day, the 3rd American Army threatened the Frankfurt Corridor between the cities of Mainz and Worms, through which German supply lines ran. While the Germans attempted to do something, the 7th Army took Saarbrücken and rejoined the 3rd Army. A part of the Germans retreated to the Eastern shore of the Rhein.

The value of self-propelled armoured vehicles was seen very quickly by European armies. The army of the young Soviet republic was no exception. In 1918, Lenin, speaking to the delegates of the Emergency All-Russia Soviet Assembly highlighted that a victorious army does not only have the braver soldiers and more talented commanders, but superior equipment.

Armoured cars and trains were used actively by the Red Army. It was not so with tanks. No domestic tank building school existed and there were few captured vehicles. A foundation for creating a new tank was needed. The captured Renault FT-17 was such a foundation. One of four tanks captured at Berezovka station near Odessa was sent to Lenin by the Second Ukrainian Soviet Army. The FT-17 was one of the most advanced vehicles available at the time. Its design was the first to use a layout later judged as classic: rear engine compartment, middle fighting compartment, armament in a rotating turret.

After the captured Renault participated in a May Day parade on Red Square, it was sent to Nizhniy Novgorod, to the Krasnoye Sormovo factory. The factory engineers, directed by I.I. Hrulev and F.I. Nefedov designed blueprints and tools for a "Russian Renault". On August 21st, 1920, the first output of the Soviet tank industry started trials: the 7-ton "Freedom Fighter Comrade Lenin".

The main value of the Russian Renault for the USSR lay in the experience obtained during its design and production. Later, it was used when creating the first truly mass produced Soviet tank, the MS-1.

The Spanish Civil War began on July 17th, 1936. The conflict was between those on the side of the Spanish Republic and Francisco Franco's nationalist forces. The Republicans were supported by the USSR and Mexico, while the Francists received military aid from Germany, Italy, and Portugal.

After defending Madrid in the late fall of 1936, Republican forces, lacking highly trained and disciplined troops, spent time to rebuild their forces. On December 19th, 1936, the rebels resumed their offensives. After heavy battles at Brunete and the valley of the river Jarama, the position of the front stabilized.

The Italians attempted to shift the balance in the favour of the Francists. On March 8th, they performed an offensive with the "Black Flame" division. To develop this offensive, the division would be joined by another Italian division and a Spanish brigade. The Spanish-Italian forces had CV-3/33 and CV-3/35 Italian tanks, about 150 vehicles in total. In order to contain the attack, the Republicans transferred 20 T-26 tanks and two international brigades from Jaram to Guadalajara. Soviet tankers drove the tanks, and the battalion was commanded by Major M.P. Petrov.

On March 13th, 1937, the second stage of the battle began. Enrique Líster's 68th International Brigade and the tank battalion took advantage of the Italians' slow deployment and struck their enemy. As a result, the Republicans dealt a large blow to the Italian regiment, took trophies, and captured the city of Brihuega.

At the same time, on the opposite flank at Torro del Burgo, the 35th Republican Brigade also pushed away its enemy. By the evening of March 13th, the position of the Republicans on the front was much more solid.

From March 14th to March 17th, the Italians tried more attacks. Thanks to the Republican reserves, and uncontested superiority of T-26 tanks over Italian tankettes, these assaults had no success. Italians took serious losses and had to retreat. The Republicans won that battle.

"Commanding a platoon of small tanks during an attack on the village of Chemodanovka near Akhtyrka, comrade Choboyan showed daring and courage, personally suppressing an AT gun. Comrade Choboyan noticed a German Tiger tank, let it come close, and knocked it out, following up by suppressing several enemy MG nests and leading an attack on Chemodanovka. His infantry did not move up with tanks. Comrade Choboyan left his tank and personally raised the infantry and led them into an attack, during which he was wounded in the head. He did not leave the battlefield until Chemodanovka was taken.

Or his courage and resilience, comrade Choboyan is worthy of a government award, the Order of Lenin.

Wow, a T-70 taking out a Tiger! That's quite a feat for a tank one sixth of the mass. How did it manage? Schneider shines a light on what could have happened.

"23 August 1943: Two Tigers push back several attacks together with other tanks of the regiment east and northeast of Michailowka (twelve kilometers southeast of Achtyrka)...The main gun of one Tiger is put out of action."

Saturday, 29 March 2014

The columns are as follows: number, part number, part name, mass in kilograms (in the 1937 model), number of units per vehicle, cost in 1939 roubles, and notes. The note is only one: the vehicle as repaired and used model 1939 radiators.

Friday, 28 March 2014

Many vehicles were sent to the Soviet Union, underwent trials, and then were not selected for further orders. The M18 Hellcat (or T70 GMC, since this particular vehicle predates the standardization under the name "M18") was one of them.

"Summary

The American T70 SPG cannot be recommended for import for the following reasons:

Light armour, protecting from only rifle bullets and small shell fragments.

High fuel consumption:

Highway: 78.5 L/hour

Dirt road: 80.5 L/hour

Off-road, over snow: 130.7 L/hourThis is several times higher than the fuel consumption of other vehicles of this class in the same conditions.

Using high quality gasoline as fuel makes the SPG fire prone.

The off-road performance is poor.

Conclusions

A series of trials of the American T70 SPG determined that:

The maximum speed is 75.6 kph.

Sharp braking of the vehicle in motion faster than 45 kph results in skidding.

Average speed:

Highway: 43 kph

Dirt road: 23.8 kph

Off-road, over snow: 19.4 kph

The speed of the vehicle on a paved road is limited by its insufficient stability, especially on a highway coated with iced over snow.

The speed of the vehicle on dirt roads and snow is limited by the impossibility of using higher gears, due to insufficient flywheel moment produced by the hydraulic transformer.

The fuel consumption is:

Highway: 78.5 L/hour

Dirt road: 80.5 L/hour

Off-road, over snow: 130.7 L/hourWhich is several times higher than the fuel consumption norms of vehicles of this class.

The vehicle cannot cross roadside ditches or large craters due to insufficient flywheel moment of the hydraulic transformer.

The maximum grade the vehicle can climb on iced over ground is 16 degrees. Higher grades cannot be climbed due to tracks losing contact with the ground. In identical conditions, the SU-76M can climb up a 26 degree grade.

The maximum acceptable grade for going downhill is 24 degrees on snow.

The vehicle cannot tow other vehicles of the same weight class on difficult terrain due to insufficient flywheel moment of the hydraulic transformer.

The maximum tilt angle before the vehicle slips is 18 degrees.

The maximum fording depth over solid ground without preliminary preparation is 1.55 meters. Larger depths cannot be forded due to water entering the engine compartment through the engine grille.

The gun has good precision. At a range of 1200 meters, average horizontal deviation is 0.16 meters and vertical deviation is 0.1 meters.

The muzzle velocity of the AP-tracer shell is 803 m/s.

The angle of flight of the AP shell is negative: -3.6 degrees.

The SPG has adequate stability when firing. After firing, the vehicle recoils negligibly.

After a shot, the aiming offset is insignificant, 0-005 elevation, 0-02 traverse.

Firing from short stops is possible and effective.

Firing on the move is ineffective.

The maximum rate of fire of the SPG is 11.4 RPM.

Aimed rate of fire:

Without shifting targets: 9.7 RPM

With shifting targets: 7.7 RPM

The maximum force on the aiming mechanisms while the vehicle is in a horizontal position is 1.0-4.5 kg for elevation, 1.5 for turret traverse.

All gun mechanisms worked flawlessly and had no defects.

The gunner's position is comfortable.

The loader's position is cramped, and does not allow for efficient operation.

The commander's position, due to a lack of commander's periscope, and insufficient protection from shell fragments and bullets, does not provide for comfortable and safe work.

The driver's position and the position of his assistant are comfortable. Both crewmen can shift gears.

The ammunition rack is inconveniently placed. Out of the 45 shells, only 9 are readily available for the loader. The rest cannot be swiftly used for shooting.

The vehicle is reliable. No components or mechanisms of the vehicle broke during trials.

In difficult terrain conditions, the hydraulic transformer does not fully pass on the flywheel moment from the engine to the transmission, reducing the speed and fuel economy of the vehicle.

The double differential reduces maneuverability and stability of the vehicle.

The attachment of idlers and drive wheels ensures that tracks are taut regardless of the road conditions.

The silent block connectors of track links prevents wear of the track pins.

Thursday, 27 March 2014

The completed work on increasing the power of the self propelled D-5 gun is analogous to that done by factory #8 on the 85 mm AA gun. It is important to note that we started working on increasing the muzzle velocity to 900 m/s before the start of the war in 1941, when we designed and partially completed the U-15 gun system mounted on the M-30 mount. The system was designed to combat enemy tanks. As the issue was solved with other artillery systems,work on the U-15 was never completed.

Currently, the factory received instructions to continue on this path of increasing the power of the D-5 gun by lengthening its barrel and increasing the density of loading, with the condition of retaining the current shell.

The barrel, chamber, and the dimensions of the D-5 system were borrowed from the 85 mm AA gun, as was the ammunition it uses.

The barrels of the 85 mm AA gun, and therefore the D-5 gun, are characterized by a small chamber, about 19% from the overall distance travelled by the shell. Usually, this distance ranges from 20 to 25%. The increase of this gun's power could not be very large, since the weight of the shell could not increase very much, and the density of loading could only be increased from 0.62 to 0.76. The barrel was lengthened to 64 calibers. The muzzle velocity reached was 900 m/s, with the pressure in the barrel of almost 3000 kg/cm^2 and chamber size of 14.5%.

If for the AA gun, the barrel length can be increased further, but the use of a tank gun with a longer barrel is not convenient. A more reasonable modernization of the D-5 gun would be the adoption of a longer one-piece round, the size of which would allow for increasing the gunpowder charge.

The D-5BM system increases the muzzle velocity by 108 m/s, or by 13.5%. It may be raised to 910 m/s by increasing the pressure slightly, to 3000-3100 kg/cm^2. The robustness of the barrel and other mechanisms allow for this.

In this case, the increase of the shell velocity compared to the D-5 gun would be 118 m/s, or almost 15%. We expect the penetration to increase by the same amount, using Krupp's formula.

The D-5BM gun has the advantage of preserving ammunition capacity, due to the same size shell. The ammunition rack size would be decreased when using a more powerful shell of the same caliber. Another advantage is that the shell only becomes 0.5 kg heavier, which is insignificant, allowing the rate of fire of the system to be maintained. Both of these factors play a significant role.

Using a D-5BM shell in a D-5 system allows the increase of the muzzle velocity by 40-45 m/s, which will cause no problems with robustness.

A further rational change would be to increase the ballistics of these guns by changing to NG gunpowder, with 10% increase in power and nearly 5% increase in the shell's initial speed.

Wednesday, 26 March 2014

Even though an 85 mm tank gun was not put into production until 1943, experiments with guns of these calibers predate the invasion of the Soviet Union. Before Tigers and Panthers hit Russian land, engineers knew that anti-tank guns must constantly evolve. The U-10 was one such proposed design.

"In addition to my letter #1546s from November 3rd, 1941, I deport that the U-10 divisional gun, created by placing an 85 mm model 1939 gun barrel on a 122 mm model 1938 (M-30) howitzer mount, has been tested at the Ural artillery proving grounds on October 18th, 20th, 21st, and 25th (see report #1998 from the Ural proving grounds in 6161s from November 9th).

Aside from the above trials, the experimental U-10 prototype is undergoing trials by the commission you appointed, led by Military Engineer 2nd grade, comrade Sorokin.

200 shots have been fired from the gun, and it has been towed 300 km by a 3-ton ZiS-5 truck.

Trials showed that:

The precision of the gun gives better results than existing anti-tank and divisional guns.
At 1000 meters, average vertical deviation is 0.2 m, horizontal is 0.17 m.

At 2000 meters, average vertical deviation is 0.35 m, horizontal is 0.42 m

The system is stable when firing from dirt or from concrete.

After 300 km of towing (900 km total), a leaf spring broke. When the system was taken apart, it was discovered that the semi-automatic mechanism casing burst. This could only happen after firing several rounds with a muzzle velocity of 850-860 m/s and maximum chamber pressure of 2850-3000 kg/cm^2 (stock muzzle velocity is 800 m/s and maximum pressure is 2535 kg/cm^2).

The spring was replaced, and the commission continues testing. The system will be towed with a limber by a tractor and a car, as well as a horse.

A broken spring after 900 km of poor, bumpy roads is not a reason to delay the U-10 battery sent to the army according to the GAU KA Chief, Colonel-General of Artillery, comrade Yakovlev.

The issue of reinforcing the spring or including spares will be resolved upon the completion of trials by the current commission.

The 85 mm gun on the M-30 mount (U-10) has many positive qualities, giving it a right to be adopted into divisional artillery. Th U-10 gives the division the ability to combat powerful enemy tanks. Its good stability and gun shield give it an advantage over the 85 mm AA gun. A U-10 gun in a division will be used in its intended role.

The gun's higher mobility caused by its smaller weight, lower time to battle readiness, and same rate of fire as the AA gun allows units greater mobility when fighting tanks.

The U-10 gun is easier to produce than the AA gun, and its production will cause no additional difficulties.

I send you the technical documentation for the U-10 gun, received from the factory in #F-609/63ss on November 23rd of this year. Pending completion of the trails by the commission led by Military Engineer 2nd grade comrade Sorkin, I deem it possible to raise the question of adopting the U-10 to the GKO."

In October of 1941, Uralmash, on its own initiative, produced a new 85 mm U-10 divisional gun.

The new gun is built by placing the oscillating part of the 85 mm model 1939 AA gun on a model 1938 howitzer mount.

The experimental prototype of the U-10 gun underwent gunnery and mobility trials at the Uralmash factory and Ural proving grounds in the presence of Army General comrade. Tulenev and Lieutenant-General comrade Sivkov. Brief information on the results of the trials are included in letter #1546 from November 3rd, 1941 from the regional engineer at UZTM, Military Engineer 1st grade, comrade Firsov. The same letter informs us that according to the orders of comrade Yakovlev, a battery of 4 of these guns is to be sent to the acting army.

According to orders of Major-General comrade Hohlov, the 4 U-10 guns will be sent to base #36 to be assigned to the Chief Quartermaster of Artillery of the Moscow Military District for trials and combat work on the front. At the same time, the Chief Quartermaster was sent a letter #790030 on November 10th, 1941, titled "List of main questions that should be answered after frontline trials of U-10 guns:, confirmed on November 13th by Major-General comrade Hohlov.

On December 9th, 1941, letter #1691ss was received, sent on November 28th, 1941 by the UZTM regional engineer containing trials materials by the commission led by Military Engineer 2nd grade comrade Sorkin. Due to the new re-organization of GAU, I am sending these materials to you. No information has arrived regarding the combat use of the experimental U-10 85 mm guns has arrived at GAU."

As we haveseenbefore, "powerful enemy tanks" failed to materialize, and the gun never reached production. However, the barrel of the 85 mm AA gun returns to a dedicated anti-tank role (much like the Germans, the Soviets used their high caliber AA guns in direct fire roles when necessary) in 1943, when the SU-85, IS-1, and T-34-85 are produced, and then as a divisional D-44 gun in 1944.

Tuesday, 25 March 2014

When talking about armoured forces, people often brag about the thickness of armour on the tanks of their favourite army, perhaps the caliber of the guns, or speeds of the tracks. Often, the recovery vehicles and the actions of the engineers and repairmen are ignored. Unjustly so.

This graph shows the number of working tanks in possession of the 1st Guards Tank Army during two operations, the Belgorod-Kharkov operation (dashed line) and Lvov-Sandomierz operation (dashed-dotted line). To highlight the effort of the engineers, two more lines are included for the two operations. The solid black line shows the amount of working tanks minus the amount of repaired tanks for the Belgorod-Kharkov operation, and the double black line does so for the Lvov-Sandomierz operation. As you can see, the efforts of the repairmen managed to keep the army at about one third to one half strength, while in their absence, the armies would be devoid of tanks two weeks into the fighting.

Sunday, 23 March 2014

I already covered light and medium SPGs, so let's move on to heavy SPGs in CAMD RF 38-11369-1.

"Experimental work on heavy SPGs.

The creation of heavy artillery SPGs follows the goal of increasing the firepower of tanks. Since placing 152 mm guns in the turrets of existing tanks was not possible, it was deemed reasonable to place these artillery systems in immobile fighting compartments. In order to preserve the production numbers of SPGs at tank factories, the overall component layout was preserved. As experience showed, unification of tanks and SPGs was very effective. It was possible to set up mass production in very short amounts of time with minimal decrease in production numbers. In order to fill the Red Army's need for new heavy SPGs, the following work was done.

1. On the ISU-152 SPG.

According to GOKO decree, in December-January of 1942-1943, the SU-152 was designed and built by the Kirov factory. The SU-152 SPG consists of a 152 mm gun-howitzer on a KV-1S chassis. The SPG was tested in January-February of 1943. GOKO decree #2883 on February 14th, 1943 adopted the vehicle into the Red Army.

Mass production SU-152 produced by the Kirov factory

Experimental ISU-152 SPG produced by factory #100

According to a State Committee of Defense decree, factory #100 designed an experimental ISU-152 SPG in June-September of 1943. The ISU-152 consisted of a 152 mm ML-20 gun on an IS tank chassis. In October of 1943, the SPG underwent trials at NIBT and GANIOP proving grounds over 430 km and 303 shots.

Combat mass: 45.5-46 tons

Crew: 5

Front armour: 60-100 mm

Side and rear armour: 60 mm

Armament: 152 mm ML-20 gun-howitzer

Muzzle velocity: 600 m/s

Horizontal traverse: 10 degrees

Vertical traverse: -3 to +20 degrees

152 mm shells: 20

Average highway speed: 23.4 kph

Maximum speed: 37.5 kph

Average off-road speed: 18.2 kph

Engine: V2-IS

Maximum engine power at 2000 RPM: 520 hp

Fuel type: diesel

Fuel capacity: 500 L

The experimental ISU-152 SPG passed trials and was recommended for adoption by the Red Army. The ISU-152 was adopted into the Red Army by GOKO decree 4504ss on November 6th, 1943, and is still produced at the Kirov factory.

Compared to the SU-152, the ISU-152 has stronger armour and a more robust transmission, engine, and suspension design. The armament was unchanged, as the ML-20 was powerful enough for any application. The ammunition rack, sights, observation devices, among other components, were also improved.

Engineer-Major comrade Rabtsev worked admirably in designing the ISU-152 SPG. As a part of a commission led by Engineer-Colonel comrade Demyanenko, comrade Rabtsev corrected several defects in the ML-20 gun mount.

2. On the ISU-122 and ISU-122S SPGs.

An experimental prototype of a heavy SPG with a 122 mm A-19 gun instead of the ML-20 was built by factory #100 in December of 1943. The work was conducted in agreement with USA GBTU to increase the anti-tank power of the SPG. This was achieved by replacing the 152 mm gun barrel with the 122 mm A-19 barrel. The gun mantlet and ammunition rack were changed, without alterations to any other components of the production SPG.

With the installation of a 122 mm gun, the following was achieved:

High penetration. 122 mm shells with a muzzle velocity of 800 m/s penetrated thick armour, which was necessary in battle with German tanks and SPGs.

High rate of fire and precision. The rate of fire of the A-19 was twice as high as the rate of fire of the ML-20.

Increase of the ammunition rack from 20 shells to 30 shells.

Reduction of the combat weight due to a lighter gun system.

Trials of the ISU-122 were conducted at the Gorohovets proving grounds from December 24th to December 31st, 1943 over 463 shots by a commission led by Major-General of the tank engineering service comrade Alymov. The SPG passed trials. Based on this, the ISU-122 was recommended for service in the Red Army. By GOKO decree #5378 on March 12th, 1944, it was put into mass production at the Kirov factory.

As a result of the 122 mm D-25 gun with identical ballistics entering production at factory #100, the factory was tasked to design an SPG that uses the D-25 gun. In April 1944, the ISU-122S SPG was built. The ISU-122S is a further modernization of the ISU-122 SPG that increases rate of fire. The D-25 is designed as a tank gun, and its recoil mechanisms and breech are more compact than on the A-19. As a result of this, the crew was more comfortably placed in the fighting compartment. The shorter recoil and sliding breech (the A-19 had a screw breech) increased the rte of fire (from 2.5 RPM on the A-19 to 6 on the D-25). The unification of tank and SPG guns was also important.

The experimental ISU-122S prototype was tested at the Gorohovets proving grounds from June 2nd to June 7th, 1944, by a commission headed by Engineer-Colonel comrade Kupriyanov over 446 shots and 192 km. Tests were conducted carefully and with a high level of mastery. Due to superior qualities of the ISU-122S SPG over the ISU-122, it was recommended for adoption into the Red Army. GOKO decree #6430 on August 22nd, 1944 adopted the ISU-122S for service. The ISU-122S remains in production at the Kirov factory to this day. It is important to point out that both the ISU-122 and ISU-122S are still in production. This is due to the fact that D-25 production is insufficient to cover demand.

Mass production ISU-122 with 122 mm A-19 gun built at factory #100

Combat mass: 45.5-46 tons

Crew: 5

Front armour: 60-100 mm

Side and rear armour: 60 mm

Armament: 122 mm A-19 gun

Muzzle velocity: 781 m/s

Horizontal traverse: 10 degrees

Vertical traverse: -3 to +20 degrees

122 mm shells: 30

Maximum speed: 37.5 kph

Average highway speed: 23.5 kph

Average off-road speed: 18.2 kph

Engine: V2-IS

Maximum engine power at 2000 RPM: 520 hp

Fuel type: diesel

Fuel capacity: 500 L

Combat mass: 44.5-45 tons

Crew: 5

Front armour: 60-100 mm

Side and rear armour: 60 mm

Armament: 122 mm D-25S gun

Muzzle velocity: 781 m/s

Horizontal traverse: 11 degrees

Vertical traverse: -2 to +20 degrees

122 mm shells: 30

Maximum speed: 37.5 kph

Average highway speed: 25 kph

Average off-road speed: 18.1 kph

Engine: V2-IS

Maximum engine power at 2000 RPM: 520 hp

Fuel type: diesel

Fuel capacity: 500 L

3. On the ISU-122BM and ISU-130 SPGs.

In order to further improve the armament of heavy SPGs, the government decided to produce new 122 mm guns with a muzzle velocity of 1100 m/s and 130 mm guns with a muzzle velocity of 900 m/s. According to GOKO decree #4851 from December 27th, 1943, factory #100 produced three experimental prototypes: two ISU-122BMs and one ISU-130, equipping production SPGs with these guns.

The ISU-122BM SPGs were built wit a 122 mm BL-9 gun designed by OKB-172, and one with a 122 mm S-26-1 gun designed by TsAKB. The BL-9 and S-26-1 have identical ballistics and differ in component design. The muzzle velocity of these guns is over 1000 m/s, and 200 m/s higher than the D-25. The increase of muzzle velocity increased the penetrative power of the guns.

The experimental SPGs were late due to delays in producing the guns. The ISU-122BM with a BL-9 gun was delivered for trials on July 9th, 1944. The second, with the S-26-1 gun, was delivered to trials on November 15th, 1944, instead of April 1st, 1944, the term stated in the GOKO decree.

The ISU-130 was produced and delivered for trials on November 25th, 1944, instead of April 5th, as per decree. The prototype used a 130 mm S-26 gun designed by the TsAKB, based on the B-13 naval gun.

Trials of the three SPGs were split into three stages.

First stage: preliminary artillery trials at GANIOP in Leningrad.

Second stage: proving grounds gunnery and mobility trials. Gunnery trials are to be held after the guns pass preliminary trials.

Trials results:

The ISU-122BM with a 122 mm BL-9 gun designed by OKB-172 failed trials due to insufficient robustness of the barrel (August, 1944). A decision was made to improve the barrel and test the gun again. A new barrel was ready by February of 194. The delay with the new barrel and the S-26-1 barrel was due to the fact that NKV only produced one of each barrel. After their breakage, a lot of time was needed to make new ones.

Despite the demands of the Military Council of the Armoured an Motorized Forces of the Red Army to produce backup barrels, NKV did not do so, and did not take into practice producing experimental guns with large muzzle velocities. Delays were also caused by factories #172 and #232, which delivered poor quality barrels.

The BL-9 passed preliminary trials in 1945, from April 5th to May 30th. The ISU-122BM is currently undergoing trials in parallel with the other ISU-122BM SPG.

The ISU-122BM SPG with the S-26-1 gun failed November trials. Its barrel was also insufficiently robust. Correction of the gun took a long time, for the same reasons as above. Only by June 1945 was a new barrel installed on the SPG to make it ready to resume trials. Which of these SPGs is superior and which will be mass produced will be discovered in the near future.

With an SPG armed with a similar gun, the Red Army will gain a new powerful method to combat even heavier enemy tanks and SPGs.

Experimental prototype of the ISU-122BM SPG built at factory #100

Combat mass: ~47 tons

Crew: 5

Front armour: 60-100 mm

Side and rear armour: 60 mm

Armament: 122 mm BL-9 or S-26-1 gun

Muzzle velocity: 1000 m/s

Horizontal traverse: 10 degrees

Vertical traverse: -1 to +18 degrees 40 minutes

122 mm shells: 20

Maximum speed: ~37.5 kph

Average highway speed: 23.4 kph

Average off-road speed: 18.2 kph

Engine: V2-IS

Maximum engine power at 2000 RPM: 520 hp

Fuel type: diesel

Fuel capacity: 500 L

The ISU-130 SPG underwent artillery trials at the Leningrad proving grounds twice, once from November 24th to December 8th, 1944, and once from December 14th to December 31st, 1944. 663 shots were fired in total (1st stage: 359 shells, 2nd stage: 304 shells). After defects found in the second stage, the ISU-130 was returned to TsAKB to be corrected for further trials.

Despite numerous demands from GBTU, the correction took until May of 1945. Currently (June 1945) it is undergoing mobility and additional gunnery trials. The ISU-130's gun is a naval caliber gun, and has never before been used by the Red Army. However, considering the positive qualities of the 130 mm gun, it may be worthwhile to introduce a new shell caliber.

Experimental prototype of the ISU-130 with a 130 mm S-26 gun

Combat mass: ~47 tons

Crew: 5

Front armour: 60-100 mm

Side and rear armour: 60 mm

Armament: 130 mm S-26

Muzzle velocity: 900 m/s

Horizontal traverse: 7 degrees 50 minutes

Vertical traverse: +16 degrees 30 minutes

130 mm shells: 20

Maximum speed: 37.5 kph

Average highway speed: 23.4 kph

Average off-road speed: 18.2 kph

Engine: V2-IS

Maximum engine power at 2000 RPM: 520 hp

Fuel type: diesel

Fuel capacity: 500 L

4. On the ISU-152BM SPG.

The experimental ISU-152BM prototype was produced by factory #100 on its own initiative in April of 1944. This prototype used the BL-8 152 mm gun at first, then the BL-10 gun, produced by factory #172. These guns were installed in a production ISU SPG.

The BL-8 and BL-10 guns have the same muzzle velocity of about 850 m/s and identical ballistics. They differ in the breech type. The BL-8 has a screw breech, while the BL-10 has a semi-automatic sliding breech.

In July of 1944, the BL-8 gun was tested on the Leningrad artillery proving grounds over the span of 501 shots. Trials showed flaws in the gun's design. As a result of July trials, a new gun was built, indexed BL-10. In the end of August of 1944, the ISU-152BM SPG with a BL-10 gun was delivered to the Leningrad artillery proving grounds for trials. However, trials were delayed due to a delay in procuring the new type of AP shell.

In December of 1944, the BL-10 was trialled, but failed trials due to insufficient robustness of the barrel, and was sent back for corrections. Production of a new barrel was delayed due to defects at factory #172. A new gun barrel was only built and produced by July of 1945.

With the successful correction of this gun's defects, the Red Army will receive a new, more powerful, artillery system that can defeat any known or potentially built tanks and SPGs of the enemy. Aside from its AP performance, the gun has good HE performance against enemy artillery and other targets.

The SPG may be further improved by reducing the overhang of the barrel by moving the fighting compartment backward and widening the fighting compartment.

Experimental prototype of the ISU-152BM SPG built at factory #100

Combat mass: ~47 tons

Crew: 5

Front armour: 60-100 mm

Side and rear armour: 60 mm

Armament: 152 mm BL-10

Muzzle velocity: 850 m/s

Horizontal traverse: 8 degrees

Vertical traverse: -3 degrees to +18 degrees

152 mm shells: 21

Maximum speed: 30-34 kph

Average highway speed: 23-25 kph

Average off-road speed: 18 kph

Engine: V2-IS

Maximum engine power at 2000 RPM: 520 hp

Fuel capacity: 500 L

Experimental prototype of the IS-3 based heavy SPG produced at the Kirov factory

I talked about tanks with additional armour before, including the advantages and downsides of this treatment. However, there is one I did not mention.

"5 T-26 tanks belong to the 40th Tank Brigade that carry additional wartime armour screens, ## 4314, 4307, 4312, 4310, and 4394. The armour does not allow dismantling the guns on these vehicles, as the armour is welded on. The military representative of factory #174 examined the vehicle, and concluded that it is necessary to remove the extra armour, after which it will be possible to dismantle the gun.

Saturday, 22 March 2014

The M3 Lee was meant to be a stop-gap design before a "real" medium tank could be built (ie, the Sherman), but it was good enough for the sands of Africa. Sadly, the Eastern Front was a little more demanding.

Here are the Soviet impressions of the M3 Lee, or, as it was indexed in the Red Army, M3s (sredniy, medium). This particular tank was #304293, and arrived in the USSR on February 2nd, 1942.

"Design Evaluation

Both the size and design of the hull are not modern. The tank is too tall, and the vertical positioning of the armour plates (with the exception of the front ones) gives the tank poor protection against artillery fire.The inside of the tank comfortably accommodate 7 crewmen, and also can carry 10 soldiers armed with submachineguns in summer conditions. The tank can be used this way to transport submachinegunners. While carrying troops, all tank guns can fire. Dropping off the 10 soldiers through the side hatches takes 25-30 seconds. Side hatches provide convenient entry and exit for the crew and soldiers.

The periscopic sights are simple and have no original solutions. They protect the crew from bullets and provide for adequate visibility.

The machineguns and ammunition rack are placed with adequate convenience. The limited angle of traverse of the 75 mm gun (32 degrees) limits its effectiveness.

A lack of sights for machineguns placed next to the driver and in the small turret prohibits aimed fire, and forces one to question the point of such machineguns.

The engine is reliable. The use of star-shaped engines in tanks is not ideal, due to the inevitable increase in the height of such a tank. Gasoline engines, especially high octane aircraft engines, cannot meet all requirements for tank engines.The best tank engine is a diesel engine, with superior flywheel moment, higher fuel economy, lower fuel quality requirement, and, what is most important, superior fire safety.

Cooling radiators for oil in the engine and gearbox provide normal temperatures for devices in summer conditions with high external temperature. The concept of oil cooling should be more common in domestic tank building.

The rubber-metallic track has a long service life, and should be considered for implementation in domestic tank building.

The buffered spring suspension of the tank is simple, reliable, and provides smooth movement of the tank.

Track support rollers are too close to the carriers, which leads to them being packed with mud on muddy roads, stopping, and increasing wear on the tracks.

Compared to domestic tanks, it is difficult to access tank components for field repairs, but this is not a significant drawback due to the reliability of the tank in general and its separate components."

The serial number, in case you doubted the one painted on the hull. The serial number in Kubinka is erroneously written as 3011745.

And now, to the actual impressions.

"As a result of gunnery trials, it was discovered that:

The cramped crew space, inconvenient locations of the turning and firing mechanisms, wobbling of the armament and rapid oscillations of the tank make it impossible to aim on the move without the use of the hydraulic stabilizer.

When aiming with the mechanical controls, it is not possible to use the electric firing mechanisms. The mechanical mechanism does not provide timely firing of the weapon.

The sight is not tightly fixed to its mount. When pressing on it, it moves vertically by a distance corresponding to 450 yards on the sight scale.

The insignificant size of the sight markings make fire correction and aiming difficult.

Firing on the move without the stabilizer allows for a rate of fire of 3.5 rounds per minute. The use of the stabilizer increases the rate of fire to 5-6 RPM and increases precision of fire.

The hydraulic turret turning mechanism is insufficiently sensitive, and does not allow for rapid target acquisition.

Evaluation of the crew workspace:

Commander: The commander is placed in the turret, to the left of the gun. He is also the gunner. The commander is tasked with observation of the surroundings, location of targets, fire correction, and directing the actions of the crew.It is impossible to use the sight of the artillery system due to its very low position. Using the mechanical aiming mechanisms is inconvenient, and rapidly tires the gunner. The workspace does not allow for 360 degree observation.

Loader: The loader is placed in the turret to the right of the gun and machinegun. Access to the machinegun and ammunition stored in the fighting compartment is inconvenient. Access to the ammunition stored on the floor of the tank is impossible without aid of other crew members.

...

Evaluation of the combat, tactical, and usability characteristics of the M3 light tank model 1942

The tactical and usability characteristics of this tank are equal to those of the M3 light model 1941.

The cramped workspace, poorly placed mechanisms, and wobbly gun lower the combat qualities of the tank.

The hydraulic mechanism does not provide accurate aiming of the gun due to its poor sensitivity.

Using the hydraulic stabilizer in motion increases the rate of fire to 5-6 RPM and increases the precision of fire.

The small size of the periscopic sight markings make aiming and fire correction difficult.

The telescopic sight is placed very low. It is not possible to use it to fire the gun.

Access to ammunition in the fighting compartment is inconvenient. Ammunition in the hull can only be accessed with help from other crew members.

The coaxial machinegun may fire accurately only with the use of tracer rounds. The gun sight does not have a machinegun scale.

The machinegun in the driver's compartment allows for unaimed fire with the use of tracer rounds.

Due to high effective engine power, the tank moves quickly in all winter road conditions, and maneuvers well.

It is necessary to supply this tank with spurs for winter driving. Put spurs on each track link (66 spurs per track). Otherwise, the tank will shake when moving on roads in poor condition. This shaking leads to malfunctions in the tank, tires out the crew. Shaking the crew in the turret impedes the use of observation devices and gun sight. The spur attachment method is not reliable."

Tuesday, 18 March 2014

As a part of Lend-Lease, the USSR received two British 17-pounder anti-tank guns in April of 1944, which were trialled at the GANIOP between September 8th and November 10th of that year.

17-pounder on trials.

17-pounder on trials, pulled by a Studebaker US6 truck.

#9. The left trail of the gun mount is deformed.

An unfortunate event happened during the test firing: the left trail of the gun mount was dented. The dent later cracked and resulted in the trail bending. It was replaced with one from the second gun.

Some conclusions:

"The effort on aiming mechanisms is acceptable and ranges from 0.5-4 kg.

The time to go from march to firing position and back is equal to 40-60 seconds.

The gun has a series of drawbacks:

It is not possible to push the gun 500 meters by hand over rough terrain. The 7 man crew can only push the gun 100 meters on flat terrain. Pushing the gun is further complicated by a lack of convenient rails.

The gun is equipped with three different pumps: Studebaker pump for pumping air into the tires, pump for pumping fluid into the recoil mechanisms (of the GAZ-AA type), and two-stage air pump for pumping air into the return mechanism. This complicates use.

The handles of the aiming mechanisms and firing mechanisms are metallic. This leads to freezing hands.

The force required to fire is very high (up to 20-30 kg). The effort to open the breech is too high (up to 15-20 kg).

The recoil indicator is poorly placed behind the gun shield, leading to complications when controlling the recoil length.

Adding fluid to the recoil mechanism is difficult, as it requires the crew to leave the protection of the gun shield.

Observation of the results of the shot is difficult due to the smoke and dust kicked up by the muzzle brake.

The firing mechanism is unsatisfactory. Due to firing handles getting stuck on each other when the gun returns after firing, the gun cannot fire without fault.

Conclusions:

Advantages of the English 17-pounder anti-tank gun:

High penetrating power.

Fault-free operation of the recoil mechanisms and breech.

Good precision and stability.

Easy to read recoil and return gear mechanism fluid levels.

Drawbacks of the English 17-pounder anti-tank gun:

High combat weight (2860 kg).

Small coefficient of metal use (112).

Insufficient robustness of the trails.

Additionally, drawbacks stated in section 3 part 10.

Compared to our anti-tank guns, the English 17-pounder anti-tank gun is heavy to move between positions and inconvenient to transport.

Three different pumps makes the system difficult to service.

The report on trials of the English 17-pounder anti-tank gun was composed carelessly, and the report on trials of the pumps, due to an absence of one of the pumps, is inaccurate due to unfamiliarity with what each of the pumps does and the principles of filling the return mechanism with fluid or air.

Conclusions of the Artkom 2nd Department:

The penetrative power, stability, and precision of the English 17-pounder anti-tank gun makes it a powerful anti-tank gun that meets modern requirements for anti-tank artillery.However, the gun is very heavy for its caliber (2862 kg), has a low use of metal coefficient (112) and many other drawbacks, listed in section 3.

The gun has the following original components:

Separable box trails with variable cut, that curve upwards in the middle and are reinforced internally by riveted trusses.

The firing mechanism has three levers. The lever for firing by the breech operator is located above the breech on the gun mount case and works by pulling.Two levers are located by the gunner. One is mushroom-shaped in the center of the turning mechanism, and one is a lever located under the turning mechanism. The two latter levers transfer the gunner's force to the first lever.

During storage, in order to avoid corrosion, the recoil mechanisms are not filled with fluid. The barrel is held in place by a special holder.

The optical telescopic sight and vision device.

Spaced armour gun shield. The thickness of one armour plate is 6 mm.

Floating piston for separating air and fluid in the recoil brake.

Recoil and return length regulator.

The presence of three pumps in the system complicates service.

Remove the "top secret" classification from the short description received from GIARP and replace it with "for service use".

Send one copy each of the short description to the Chair of the Council of People's Commissars Technical Council, Chief of the Dzerzhinkskiy Artillery Academy, and the 15th Department of Artkom.

Print the conclusions and send to the addresses in the original.

Chief of the 2nd Artkom department, Major-General of the Artillery Service, Komarov

Monday, 17 March 2014

I wrote plenty on how to paint Soviet tanks, but recently, I came across a similar manual for American vehicles, listing what to do, and, perhaps more importantly, what not to do. Samples and a full download link below. The manual also includes tips about tarps and camouflaging aircraft.

Sunday, 16 March 2014

Production vehicle, SPG SU-122, produced by the Ural Machine Building Factory of the NKTP

According to GOKO decrees in October-December 1942, the Uralmash factory designed and built an experimental prototype of the SU-122 SPG. The SU-122 consists of a 122 mm M-30 howitzer on the T-34 hull.

From December 5th to December 19th of 1942, the SPG underwent trials at the Gorohovets proving grounds, over 430 km and 281 shots. The commission concluded that the SPG passed trials. GOKO decree #2559 on December 2nd, 1942, adopted the SU-122 SPG into the Red Army.

Experimental work on medium SPGs

1. On the SU-122M

The Uralmash factory, on its own initiative, developed a modernized SU-122M SPG. This vehicle was based on the SU-122 SPG trials, overseen by Major-General of the Tank Engineering Forces, comrade Ogurtsov.

The modernization was as follows:

Installation of a new D-11 122 mm howitzer instead of the M-30 122 mm howitzer.

Increase of the fighting compartment width by 350 mm and height by 100 mm.

Inclusion of a telescopic sight for direct fire.

Improved fuel and control systems.

In June of 1943, the SU-122M underwent trials at the Ural proving grounds over 329 shots and 859 km. The experimental prototype passed trials, but was not adopted by the Red Army, as a decision was already made to produce SU-85 SPGs that used 85 mm guns with improved anti-tank capability.

Experimental prototype of the modernized SU-122M SPG designed by the Ural Machine Building Factory of the NKTP

Combat weight: 31.43 tons

Crew: 4

Gun: 122 mm M-30 howitzer

Muzzle velocity: 515 m/s

Horizontal traverse: 20 degrees

Vertical traverse: -3 degrees to 26 degrees 30 minutes

122 mm shells: 40

Front armour thickness: 45 mm

Maximum speed: 55 kph

Average speed: 35 kph

Average off-road speed: 20 kph

Engine: V2-34

Maximum engine power: 450 hp

Fuel tank capacity: 460 L

2. On the SU-85

According to GKO decree #3289 from May 5th, 1943, the Uralmash factory developed and produced experimental SPGs in May-July of 1943.

SU-85-I, with a TsAKB S-18-1 85 mm gun

SU-85-II, with a factory #9 D5-S85 85 gun

SU-85-IV with a TsAKB S-18 85 mm gun

All of these SPGs were based on the SU-122 SPG. Over the period from July 25th to August 6th of 1943, all three SPGs underwent trials at the Gorohovets proving grounds over 500 km and 300 shots. A commission headed by Lieutenant-General of Artillery comrade Taranovich (today Colonel-General of Artillery). The D5-85S gun designed by factory #9 achieved superior results in trials.

Marshal of the Armoured Forces, comrade Fedorenko, Marshal of Artillery, comrade Yakovlev, and the People's Commissar of Tank Production comrade Malyshev visited the proving grounds in early August 1943, and agreed to the adoption of the SU-85 armed with a D5-85S gun, of which they informed comrade Stalin over the phone.

After this, Uralmash began mass production of SU-85 SPGs.

In September of 1943, Colonel-General of Tank Forces, comrade Biryukov visited the factory. According to an assignment from GOKO, he inspected the production lines, and occasionally offered help and coordination of factory #9 and Uralmash to aid in quantitative and qualitative improvements in production of the SU-85.

By his orders, one of the production SPGs was subjected to mobility and gunnery trials. The trials were conducted by Engineer-Lieutenant-Colonel Kovalev.

The tactical-technical characteristics of the SU-85 SPG were confirmed by GOKO decree #4436 on October 27th, 1943, provided to NKO (comrade Fedorenko) and NKTP (comrade Malyshev). With this new SPG, the Red Army received its first medium tank destroyer, capable of fighting new enemy tanks.

Experimental prototype of the SU-85 SPG designed by the Ural Machine Building Factory of the NKTP

Combat weight: 29.15 tons

Crew: 4

Front, side, and rear armour: 45 mm

Gun: 85 mm D5-S85

Muzzle velocity: 792 m/s

Horizontal traverse: 20 degrees

Vertical traverse: -4 to +25 degrees

85 mm shells: 48

Maximum speed: 55 kph

Average speed: 35 kph

Average off-road speed: 20 kph

Engine: V2-34

Maximum power at 1700 RPM: 450 hp

Fuel: diesel

Fuel capacity: 460 L

3. On the SU-100 SPG

Following GOKO decree #481 from December 27th, 1943, Uralmash developed and produced two SU-100 prototypes in March-May of 1944, one with a 100 mm D-10S gun designed by factory #9, and one with a 100 mm S-34 gun, designed by TsAKB. The SU-100 was based on the SU-85.

Several changes were made to the old SPG to increase its combat ability:

As requested by USA GBTU, the front armour was increased. Instead of the 45 mm armour of the SU-85, the armour of the SU-100 was 75 mm, at the same angle.

Robustness of the front road wheels was increased.

Ventilation was improved.

Gearbox was improved.

Other changes were made, 15 in total. The SU-100 prototypes were tested twice. First trials of the SU-100 with the D-10S gun were carried out by a commission headed by Colonel Rupyshev at the Gorohovets proving grounds from March 9th to March 27th, 1944. The trials lasted 564 km and 1040 shots. The SPG passed these trials. However, the commission requested that some design defects be corrected before entering production.

Secondary trials were performed by the same commission at the Gorohovets proving grounds from June 24th to July 6th, 1944.

The SU-100 prototype with the S-34 gun underwent trials. Trials were done in comparison with the SU-100 with the D-10S SPG. The SU-100 with the S-34 gun was trialled over 877 shots and 250 km, and did not pass trials. Work on this SPG concluded, as the SU-100 with the D-10S gun was more promising.

The D-10S prototype, after being corrected after March trials, was tested simultaneously. The SPG passed trials over 923 shots and 250 km, and was recommended for adoption by the Red Army.

Comrades Colonel Rypushev and Engineer-Majors Konev and Volgushev performed exemplary work during design and trials of the SPG.

GOKO decree #6131 from July 3rd, 1944, accepted the SU-100 for mass production and use by the Red Army.

Experimental prototype of the SU-100 SPG designed by the Ural Machine Building Factory of the NKTP

Combat weight: 31.6 tons

Crew: 4

Front armour: 45-75 mm

Side and rear armour: 45 mm

Gun: 100 mm D-10S

Muzzle velocity: 900 m/s

Horizontal traverse: 16 degrees

Vertical traverse: -3 to +20 degrees

100 mm shells: 33

Maximum speed: 50 kph

Average speed: 30 kph

Average off-road speed: 18-20 kph

Engine: V2-34

Maximum power at 1700 RPM: 450 hp

Fuel: diesel

Fuel capacity: 460 L

4. On the SU-122P SPG

In the end of 1943, Uralmash, on its own initiative with approval from USA GABTU, began work on equipping the SU-85 with a 122 mm gun. This work was conducted with the goal of exploring the viability of 122 mm guns on medium SPGs.

In June of 1944, a prototype was produced, indexed SU-122P. This prototype differed from the SU-100 experimental prototype only in armament. The SU-122P SPG was armed with a 122 mm D-25S gun.

In November 1944-February 1945, the SU-122P prototype was tested on the NIBT proving grounds over 1000 km, and fired 258 shots at the Leningrad proving grounds.

The pause between the prototype being ready and trials beginning can be explained by Uralmash being occupied with work on the SU-100, and did not submit the SU-122P for proving grounds trials.

Mobility and gunnery trials showed that armament of medium SPGs with a 122 mm D-25S gun is possible.

USA GBTU decided that an SPG with a rear fighting compartment be developed for this gun, as placing a 122 mm gun in a SU-85 (SU-100) SPG does not result in a comfortable placement of crew and ammunition. Work on the SU-122P ceased.

Experimental prototype of the SU-122P SPG designed by the Ural Machine Building Factory of the NKTP

Combat weight: 31.5-32 tons

Crew: 4

Front armour: 45-75 mm

Side and rear armour: 45 mm

Gun: 122 mm D-25S

Muzzle velocity: 781 m/s

Horizontal traverse: 16 degrees

Vertical traverse: -3 to +17 degrees

100 mm shells: 26

Maximum speed: 50 kph

Average speed: 30 kph

Average off-road speed: 18-20 kph

Engine: V2-34

Maximum power at 1700 RPM: 450 hp

Fuel: diesel

Fuel capacity: 400 L

5. On the SU-85PM SPG

The experimental SU-85PM SPG was produced at Uralmash on its own initiative in August-December of 1943. This SPG was composed of a production SU-85 equipped with an increased power D5-S85PM gun, designed by factory #9. Due to a longer barrel and increased density of propellant, the muzzle velocity increased to 900 m/s, as opposed to 800 m/s of the stock gun.

The SPG was trialled in January-February of 1944 at the Gorohovets proving grounds, firing 755 shots. The SPG passed trials, but due to the installation of a D-10S gun, which was significantly more powerful than the D5-S85PM gun, the need for the latter disappeared.

Experimental prototype of the SU-85PM SPG designed by the Ural Machine Building Factory

Combat weight: 29.5 tons

Crew: 4

Front, side, and rear armour: 45 mm

Gun: 85 mm D5-S85PM

Muzzle velocity: 900 m/s

Horizontal traverse: 20 degrees

Vertical traverse: -3 degrees 20 minutes to +26 degrees

85 mm shells: 48

Maximum speed: 55 kph

Average speed: 30 kph

Average off-road speed: 18 kph

Engine: V2-34

Maximum power at 1700 RPM: 450 hp

Fuel: diesel

Fuel capacity: 460 L

6. On the SU-101 and SU-102 SPGs

Following the order of GBTU, Uralmash designed two experimental SPGs with rear fighting compartments in March of 1945. The prototypes differed in armament.

The SU-101 SPG was equipped with the D-10S 100 mm gun.

The SU-102 SPG was equipped with the D-25S 122 mm gun.

At the end of April 1945, Uralmash produced the first SU-101 SPG. After 76 km of trials, design defects became apparent. The driver's compartment rapidly heated to 50-60 degrees, making it impossible for the driver to work. Other defects were also discovered.

Gunnery trials showed weakness of attachment of armoured plates, as well as insufficient robustness of some plates.

Currently, Uralmash is improving the design of these SPGs. All changes are being made to the second prototype with the D-25S gun. Factory trials are scheduled for the end of June of 1945.

The new SU-102 prototype differs from the SU-100 in the following way:

New engine and new layout of components.

Increased armour of the fighting compartment and hull.

Increased power of the gun and machineguns.

Improved performance over horizontal obstacles (trenches) and movement on forest roads due to gun position.

The production of these experimental SPGs is a step forward in the development of medium SPGs, but the SU-101 and SU-102 no longer meet modern requirements for armament, armour, and transmission design.

The new medium SPG prototypes, in addition to removal of currently known defects, require subsequent improvement in all main design criteria.